Seismic exploration commonly involves towing a marine seismic streamer behind a vessel. The seismic streamer is in the form of a series of hydrophone elements strung together within a surrounding tube or jacket. The hydrophone elements are joined by conductors for carrying data and command signals between connectors at the ends of segments of the streamer.
In the environment of seismic exploration, many segments are connected together to make the streamer array that is kilometers long. Further, such a long streamer experiences tremendous tension stress that is borne by stress members that parallel the data and command signal conductors. Such a stress member may also be referred to herein as a load bearing cable or rope. It has been found that retrieving a streamer by winding the streamer on a take-up capstan creates uneven stress on stress bearing cable members within a streamer.
In the course of deploying and retrieving a streamer, as well as during underway operations, the streamer may be damaged. A great deal of attention has been paid to developing techniques for quickly and inexpensively repairing damaged streamers, including repairing stress members that are integral parts of the streamers. Splicing of marine streamers until now has been difficult, infrequent, and generally disregarded by the users of marine streamers. Early wire rope stress member sections sometimes used crimped terminations for repair. With the advent and widespread use of light-weight, high-strength synthetic strength members, an appropriate splice method has not been utilized. Until now, no effective means has been found to repair a stress bearing cable of a seismic streamer within replacing the entire cable within a section of the seismic streamer.
In the event that a section of a streamer is damaged, close examination of all stress members is required. If a stress member has more than the allowable number of strands damaged (the number determined by the manufacturer), the section (at least the chassis) has generally been scrapped. The conventional method of chassis manufacture prohibits cost effective stress member replacement.
In order to repair marine streamers used in exploration, a device is required that will allow the repair of damaged areas of stress members by splicing the damaged areas and leaving the undamaged areas of the stress members intact. The region of the repair must have adequate break-strength and must allow for adjusting the splice length in order to equalize load sharing, thereby eliminating non-uniform loads on all of the stress bearing members. Such a splice must attain a high percentage of the stress member rated-break-strength (RBS), both in termination method and mechanical components. The splice should be dependable during all phases of normal operation; i.e., the splice should not back off or part.
Size is another important consideration in repairing a marine seismic streamer load-bearing cable. Given the geometry, weight, and volume constraints of marine streamers, such a splice should be as small as possible in order to reduce intrusion on surrounding components. Further, the splice should be very easy and quick to install, thereby allowing placement of the splice in close quarters. Finally, by minimizing the size of the splice components one also lessens the possibility of snagging the streamer with the installed splice components by handling equipment.
Seismic streamers in use today are commonly filled with a fluid that is carefully chosen to provide a very nearly neutral buoyancy. A device installed within a marine seismic streamer to repair a stress member should therefore produce minimal impact on the buoyancy of the streamer. In so doing, one should select a material that is corrosion proof, and provides low magnetic field disruption.